Quantitative determination of metals



May 17, 1960 T. L. THouRsoN 2,937,276

QUANTITATIVE DETERMINATION OF METALS Filed March 29, 1956 4 Sheets-Sheet 1 Nh. A s@ May 17, 1960 T. L. rHouRsoN QUANTITATIVE DETERMINATION oE METALS 4 Sheets-Sheet 2 Filed March 29, 1956 cull May 17, 1960 T. L. 'rHouRsoN 2,937,276

QUANTITATIVE DETERMINATION OF' METALS Filed March 29, 1956 f 4 Sheets-Sheet.- 3

9a/avena l Ffa/vil May 17, 1960 T. L. THoURsoN 2,937,276

QUANTITATIVE DETERMINATION OF METALS Filed March 29, 1956 4 Sheets-Sheet 4 44 1/Hag United St-ariS4: Patent O 2,937,276: oUANrnAnvE narra MINA 'Anon or METALS Thomas L. Thomson, Park Forest, Ill., assignmto Standard Oil Company, Chicago, Ill., a corporation of Indiana l l Application Maranza, l19st,v serial Nq. 4574,877. Claims. (Cl. 25o-43.5)

`of X-ray absorption and, more particularly, relates to asystem Vfor' quantitatively determining the concentration of tetraethyllead fluid in gasoline,

Analytical techniques have ybeen proposed heretofore lfor such determinations but-such techniques have required relatively complicated and expensive equipment, or are time consuming, and are not readily adapted to routine analysis. However, there is an ever increasing need for 'plant quality control devices and it is a primary object 'of thispinvention to provide a system which is adapted for use in the continuous determination of the concentration tif-tetraethyllead (TEL) in a owing stream of leaded gasoline. j j j vAnother object of thte inventionis to provide an im- 'proved` method and apparatus particularly adapted for .'rapid and routine analysis of .elements of high atomic weight in 'a matrix of low atomic weight. Another object kof our invention is` to provide an apparatus and method fo'rthe analysis of the concentration of tetraethyllead in gasoline without 'the necessity for preparing extracts of -the 'gasolineY and without calculations and plotting of .graphs and charts. These and other objects ofour li11- vention will become apparent asthe description thereof proceeds.

` Briey, I latt-ain the objects of theinvention by providfing a "system which is based upon the relatively large. absorption by atomic lead of the X-rays Aproducedwhen (beta particles from strontium 90 bombard a thin molybdenum foil, the X-rays from the strontiumr 90-mo1yb- 'denum foil lsource being passed throught a leaded sample of gasoline. -As the X-rays pass throughthe sample, they will be`ab'sorbed,`in part, by the gasoline, by the tetraethyllead, and by any other components present; thus in view of the relatively vlarge absorption -by atomic lead the greater'th'e concentration of tetraethyllead in the sample, the 'greater will be the absorption of the X-rays. Therefore, the intensity of the transmitted nX-rays is a function of the tetraethyllead concentration of the sample, which concentration can be determined by measuring the transmitted X-ray intensity.

lnasmuch as the transmitted X-rays are absorbed in part by the gasoline or other hydrocarbons present, the transmitted X-raymeasurementis sensitive'to the varying carbon to hydrogen ratio of different base stocks. We eliminate the sensitivity to the carbon to hydrogen ratio by producing X-rays whose effective wave length is about 0.6 A. X-rays whose wave lengths are `shorter than about 0.6 A. are produced bythe more energetic beta particles from the strontium 90 Iand we can reduce the beta particle energy by interposing an attenuater composed Vof low atomic number lelements such as l carbon between the 'strontium 90 'and the molybdenum foil target. y

` To permit a continuous determination in terms of vol- 4urne concentration in different base stocks, it is necessary 'that a density-'correction be made. This can be done automatically by employing a density gauge and transducer, *the-'output signal of which may be supplied to 'a computer 2,937,276 l ParentedMay 17,1960

. 2 Y or maybe used 'to adjust rthe ,position ot'a compensating wedge in the X-'ray,beam. A i l Further details of construction and advantages of my system will be given in conjunction with the description of the accompanying drawings .illustrating preferred embodiments of the invention and wherein:

yFigure 1 isa schematic diagram of an ployin'gan'X-ray source; l v

j VFigure 2 is a front elevation; l I

`Figures-3 andf4 are'vertical sections of thev apparatus ofFigure2; .-v

Figure 5 isa section taken along-S--S in Figure 4; lFigure L6'is a fragmentary view of the apparatusfot Figure 2; i

apparatus em- Figure 7 is an enlarged detail of elements in Figure 2; Figure 8 is'a'schematic diagram of a second vembodiment of our invention applied toa continuous system and including means kfor making a density correction;

' Figure 9 is an elevation schematically illustrating a density gauge for use inthe apparat-us of Figure 8; and

Figure l0 illustrates thecircuitry Ifor the density gauge Iand compensating wedge control. v

rReferring to the d-rawings, the X-ray source 10 comprises a beta ray emitter 1-1 which is a radio isotope such as strontium 90, a beta ray attenuater 12, and a foil target 13 from which the X-rays are emitted. The beam from the source 10 is passed through the sample cell 14 and the transmitted X-ray intensity measured by the detector, and associated current measuring or pulse counting circuitry represented by 15. The current measuring means may comprise an ionization chamber and the pulse counter a `Geiger tube. 4Circuits including such components are well known to the art and Willpnot be described in detail herein.

' Referring to Figures 2 to '7, the` housing 16 (includes.

three compartments; the detector tube shield 17, the sample cell ,chambery I8, and theradiation source housing 19,.r The sample'cell chamber 18 is provided with an indexed holderlf yfor positioning the sample cell 14 in alignment with the radiationvsource 10 and the detector 21. l Y, v

The shield or housing '19,for Ythe sourcev 10 encloses a .rotatable body L22 provided withr shaft z3.' within .the body 22 lis vdisposed the source 10` which is comprised of the beta ray emitter 11 and thetoil target 13. AA knob 24 is provided for rotating the shaft 23 supporting the body 22 within the shield 19 so as to expose the radiation source 10.to the sample cell 14. Y l

The sample chamber 18 is provided with a door 25. The shaft v2.3 for rotating the radiation source body y22 carries a rotatable disc 26 having a chordal section cut away to permit the opening of the door 25 only when the radiation source 10 is inits shielded position. To prevent exposing the source 1'0 within the rotatable body 22 it the door 2S has not been closed we may provide a;recessed Vand spring -loaded pin means 25a. When the door 25 is `closed, however, the pin V25a is displaced and thevdisc 26 is 'free to rotate over the outer surface of the door 2'5.

The X-ray source |10, comprising the Sr90 beta ray Vemitter 11 and the molybdenum foil target 13, is mounted Vwithin recess 22a in the rotatable body 22. This body in turn is disposed in a close vfitti-ng bore 19a within It will be understood that when the instrument is not in use or when the sample cell 14 is being introduced or removed from the sample cell 'chamber 18, ythe source -10 'is retained withinthe upper part of the housing or shield 19. y To indicate the lposition of the source wev provideanindex on the disc 26 and kalso provide-positive f 3 stop means 28 and 29 carried'by the rotatable body 22 and the lixed shield 19, respectively.

The sample cell 14 is comprised of a metal body 30, an aluminum foil 31 at the bottom, a threadedring 32 for holding the alminumwindow in place and a top ca'p 33 comprising an aluminum yfoil sheet 34, and a plastic ring in' vapor tight contact with the top of the cell. The sample cell holder 20 tits into the sample cell 18 and is provided with two tixed pins 35 which tit into matching holes 36 in the top of the detector shield 17. The curvature of the back wall of the sample cell holder 20 matches the curvature of the sample cell 14, this curvature along with a spring load pin means 37 in the sample cell holder 20 provides exact and reproducible positioning of the sample cell 14. The base of the holder 20 is provided with la port 38 which is aligned with the sample cell window 31 and the port 27 Vin the shield 19.

iter the sample cell 14 is in place, and the sample chamber door 25 is closed, the source holder 22 is rotated by means of the knob 24 on the front of the housing 19 until the source 10 and target 13 are opposite a port 27 in the bottom of the housing 19. With the source 10 in this position, the safety stop disc 26, which is attached to the knob shaft 23, prevents the sample chamber door 25 from being opened. X-rays from the source 10 can then pass through the sample cell 14. 4'

The detector tube shield 17 encloses a suitable detector means such as a Geiger-Mller tube 21 which is connected with conventional counting land high voltage equip meut. We prefer to use a Geiger-Mller tube which possesses a thin aluminum end window to pass soft radiation and should contain argon Vand krypton as the filling gas, these gases being etcient absorbers of soft radiation. The Geiger-Mller tube should be mounted so that the end window is exposed to the transmitted radiation.

'Referring to Figure 8, I have schematically illustrated another embodiment of my invention which is adapted for use on `a continuous owing stream bed. The product ows through a by-pass sample line 40 containing the sample cell 41 and a density gauge 42. The sample cell 41 corresponds to sample cell 14 in Figure l and la double faced X-ray source a is provided. The beta ray -emitterlla is preferably `a two-sided strontium 90 source prepared in accordance with U.S. Patent 2,700,111. On each side of the source 11a is a molybdenum target 13u. Radiation from one side of the source 11a is transmitted ,through the sample in sample cell 41 to an ionization chamber 43. Radiation ifrom the opposite side of the source 11a passes through a standard ,plastic wedge 44, and an aluminum wedge 45 to a second ionization chamber 46.

The current from the two ion chambers 43 and 46 are matched in opposition, each being provided with a high voltage D.C. power supply 47 land 48 which are of opposite polarity. The diierence current from the ion cham- "bers 43 and 46 is fed to a conventional and commercially available electrometer amplifier 49. The output current from the electrometer amplifier 49 is fed to a servo amplitier 50 which in turn is connected to the servo motor 51 for positioning the aluminum wedge 45 in the beam from the source 10a until the current from the two ion chambers 43 and 46 vare equal. The TEL content of the sample 'within sample cell 41 is then determined from Vthe position of the aluminum wedge 45. Also connected Vto the shaft ofthe servo motor 51 is the slide wire of a vlinear multi-turn potentiometer 54 and connected across fthe end terminals of the potentiometer is a constant D.C.

vvoltage supply 55. The voltage .between the slide wire and one of the end terminals corresponds to the position of the aluminum wedge 45. This voltage is fed to a suit fable recorder 56 which is calibrated in terms of ccs. of

tetraethyllead per gallon of sample gasoline.

y 4 so is illustrated in Figure 8. requires -a device which will measure density and put out `a signal which is a function of density. The details of one form of the density 4gauge and control circuitry for effecting such automatic correction is shown in Figures 9 and l0.

T he density gauge 42 includesla chamber 60 having an inlet 40a and .an outlet 4017 which may-be connected for ow from the sample line 40. lA float 61 connectedto a shaft 62 is disposed vwithin the chambenil and a bellows .63 lixed about base 66 of the chamber 60 acts as a packing gland for the shaft 62. The transducer 52 ismounted by fixture 67 on thebase 66, the displacement'of the o'at 61 adjusting the transducer 52 through the shaft 62. The apparent weight of the ioat 61 varies with changes in the density of the liquid flowing through the chamber 60 -and this apparent weight is impressed on the transducer 52 by means of the shaft 62. This-changes the output voltage and for a given input voltage, the output voltage depends upon the apparent weight of the oat 61 which, in turn, depends upon the density of the liquid sample under test. However, the -force constant of the bellows 63 must 4be much less than that of the Vsuitable mechanical linkage 69, positions the plastic absorber wedge 44. The motor 53 also moves the slide wire of a potentiometer 70 until the output of the transducer 52 is zero. The shaft position of the motor 53 is then a function of the density of the sample in'chamber 60 and the wedge-shaped plastic absorber 44 is moved into or out of the referenceV beam from the source 10A to compensate lfor any changes in sample density. Accordingly the position of the aluminum wedge 45 is directly related to the tetraethyllead concentration of the sample. Reverting to the transmission type targets, it is preferred to use molybdenum foil having a thickness of -about .001 inch to about .005 inch. In the embodiment parable to foils of molybdenum. .It is also contemplated that metals lying near and between silver and molybdenum in the periodic table and/or combinations of such elements in the form of alloys or larninationsl can be used as the target. Similarly, salts or other chemical compounds of these elements may be useful incertain applications of my technique.

Determinations of vtetraethyllead in gasoline samples have been made employing the apparatus illustrated in Figures A2 to 7 inclusive with the beta ray emitter 11 com'` prising a l13.5 millicurie Sr source, a 0.001 inch molbdenum target 13, and a krypton filled Geiger tube 21. The overall dimensions of our housing 16 are' about 12.75 inches by 3.25 inches by 3.25 inches. l

The results obtained were compared with concentrations determinedwby the conventional X-ray photometric apparatus which uses an Xray tube and high voltage generating equipment. Our values differed from the.true values by an average of 0.04 cc. TEL/ gallon which about the probable error of the X-ray tube method. However, our apparatus is much less expensive, and is readily portable as compared to the X-ray tube apparatus; in addition our system has the advantages of rapidity and simplicity over the wet chemical methods of analysis. l

Although we have described the invention in terms of specific examples and operations which have been set forth vin some detail, it is to be understood that these are by way of illustration only and that our invention is' not limited thereto. Alternative embodiments of apparatus and variations in operating techniques -will become apl parent to those skilled in the art in view of our discloslu'e.

To do this automatically,

Accordingly, modications in the invention and the mode of using the apparatus are contemplated without depart ing from the spirit thereof.

What I claim is:

1. A system for determining the concentration of a known metal in a flowing hydrocarbon sample stream which comprises a pair of spaced ionization chambers arranged face to face, a source of X-rays disposed between said ionization chambers, said X-rays being substantially insensitive to carbon to hydrogen ratio of the sample, sample cell means adapted to flow a sample stream between said source and a first of said ionization chambers, first movable wedge means interposed said X- ray source and the second of said ionization chambers,

means responsive to the diierential of said radiation reaching said ionization chambers, density gauge means responsive to changes in the density of the sample under test, a second wedge means interposed said X-ray source and the second of said ionization chambers, drive means for said second wedge, and transducer, means responsive to said density gauge means controlling said drive means, whereby a radiation absorption measurement indicating the concentration of the metal in the sample is compensated for changes in a sample density.

2. The system of claim l wherein the density gauge comprises a ow chamber, a oat in said chamber, and a shaft means moved by said float to actuate said transducer.

3. An apparatus for continuously determining the concentration of tetraethyllead in a owing hydrocarbon sample stream which comprises means for subjecting such a owing sample to X-ray radiation, said radiation being substantially insensitive to variations in the carbon to hydrogen ratio of the sample, means for simultaneously subjecting a variable standard absorber to like X-ray radiation, means for varying the standard absorber to equal the absorption by the sample, electrical circuit means responsive to radiation not absorbed by the sample, means for continuously obtaining an electrical quantity corresponding to changes in density of the owing sample, and means for further varying the efficiency of the standard absorber to compensate for changes in density of the sample.

4. The method of continuously determining the concentration of tetraethyllead in a owing hydrocarbon sample stream which comprises subjecting a flowing sample stream to X-ray radiation, said X-rays being substantially insensitive to carbon to hydrogen ratio of the sample, simultaneously subjecting a variable standard absorber means to like X-ray radiation, varying a portion of said absorber means to equal the X-ray absorption of the sample stream, continuously monitoring the density of the sample stream and obtaining an electrical quantity corresponding to any changes in density, adjusting the etliciency of another portion of said absorber means in re' sponse to said electrical quantity thereby to compensate for changes in density of the sample stream, and recording the adjusted position of said iirst portionof the said standard absorber as a measure of the concentration of tetraethyllead in said sample stream.

5. The apparatus of claim 3 wherein said variable standard absorber comprises an aluminum wedge portion and a plastic wedge portion.

References Cited in the le of this patent UNITED STATES PATENTS 2,467,812 Clapp Apr. 19, 1949 2,586,303 Clarke Feb. 19, 1952 2,757,290 Jacobs et al. July 31, 1956 2,844,066 Friel July 22, 1958 

4. THE METHOD OF CONTINUOUSLY DETERMINING THE CONCENTRATION OF TETRAETHYLLEAD IN A FLOWING HYDROCARBON SAMPLE STREAM WHICH COMPRISES SUBJECTING A FLOWING SAMPLE STREAM TO X-RAY RADIATION, SAID X-RAYS BEING SUBSTANTIALLY INSENSITIVE TO CARBON TO HYDROGEN RATIO OF THE SAMPLE, SIMULTANEOUSLY SUBJECTING A VARIABLE STANDARD ABSORBER MEANS TO LIKE X-RAY RADIATION, VARYING A PORTION OF SAID ABSORBER MEANS TO EQUAL THE X-RAY ABSORPTION OF THE SAMPLE STREAM, CONTINUOUSLY MONITORING THE DENSITY OF THE SAMPLE STREAM AND OBTAINING AN ELECTRICAL QUANTITY CORRESPONDING TO ANY CHANGES IN DENSITY, ADJUSTING THE EFFICIENCY OF ANOTHER PORTION OF SAID ABSORBER MEANS IN RE- 